As described in Patent Document 1, conventionally an electric motor such as a servo motor, etc. has been used as an actuator for moving joints of a robot. This is because motors are relatively readily available. However, motors have a problem that the whole robot becomes larger, and also, because they are relatively weighty, design of mechanical strength of a robot becomes important. A fluid cylinder such as an air cylinder, etc. has advantages, as compared with motors, that it is small and light, and being simple in structure, maintenance is easy, so that it is considered that the fluid cylinder is useful for the actuator for a robot.
Patent Document 2 describes an actuator previously proposed by one of the inventors of the present application.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-311667
Patent Document 2: W02005-45257